Replaceable filters for portable box fans are known. Examples include: U.S. Pat. No. 4,781,526 to Mead (bracket structure mounted on fan for receiving a filter in sliding fashion); U.S. Pat. No. 7,393,272 to Sundet (adhesive-attached hooks mounted on the sides of the fan, with elastic straps extending through the hooks to hold a filter to the face of the fan); U.S. Pat. No. 6,527,838 to Volo et al. (stick-on right-angled brackets mounted on the fan with adjustable clearance to snugly hold filters against the faces of a fan); U.S. Pat. No. 8,137,426 to Whittemore (filter frame removably mounted against the face of a box fan with straps or cords to receive a filter).
Despite these previous attempts to provide convenient air filtration on portable box fans, I am not aware of any commercially viable products. This indicates to me that these previous attempts have not been found to be sufficiently functional, convenient, aesthetically acceptable, or economical.
Accordingly, I have invented a filter attachment apparatus that solves the apparent problems with the prior art filter attachment kits.